Flight Question Phobos/Deimos landig

[exe-c]

Hi all! :hello:
As I noticed landing on this moons is more like docking then landing, BUT without a 'targets' like '-V' or '+V' assists to achive null relative speed with space stations. So how to achive it? I tried using TransX and flight directly to it - than i can land firing a hovers but can't select a location to land. I trying to use an iss-docking like style with align&sync orbits but then i can only fly by it. Is there any 'checklist' of how to land to desired base on phobos/daimos?

 

[Ark]

Transfer out to it, use the orbit MFD to pull up next to it with next to zero relative velocity, then you can practically use your RCS to fly around it and look for a landing zone.

 

[exe-c]

use the orbit MFD to pull up next to it with next to zero relative velocity

Thx, but can you explain this moment a bit more? Where can i see relative velocity? Am i right that i must meet it on peregei or apogei and then rise another point to phobos orbit by prograde burn?

 

[PeterRoss]

I guess he meant you should select Phobos (or Deimos) as a reference body in OrbitMFD, then pass through periapsis and lower your velocity (Vel on Orbit MFD) to zero. Since Mars will be the real mass center for this system it would be quite an interesting manoeuvre. I'll try it as quick as I'll make it to Mars.

 

[Kaito]

if you're using the DGIV, pro500spec0 will null your relative speed

 

[exe-c]

if you're using the DGIV, pro500spec0 will null your relative speed

Nope!

During my accidental landing to a Daimos base (just luck) i tried it! And I noticed that it works only with vessels! Bases in the DG-IV package is both base and vessel but this autopilot didn't work with planets or normal spaceports. I see only a messege that there are no target.

I use this bases [ame="http://www.orbithangar.com/searchid.php?ID=4138"]Phobos (Originally by Toni Ylisirnio)[/ame]

---------- Post added at 11:17 PM ---------- Previous post was at 11:17 PM ----------

I guess he meant you should select Phobos (or Deimos) as a reference body in OrbitMFD, then pass through periapsis and lower your velocity (Vel on Orbit MFD) to zero. Since Mars will be the real mass center for this system it would be quite an interesting manoeuvre. I'll try it as quick as I'll make it to Mars.

Thx for repling I'll try it... few minutes later

 

[Ark]

I guess he meant you should select Phobos (or Deimos) as a reference body in OrbitMFD, then pass through periapsis and lower your velocity (Vel on Orbit MFD) to zero. Since Mars will be the real mass center for this system it would be quite an interesting manoeuvre. I'll try it as quick as I'll make it to Mars.

Yeah, set reference to Phobos and when you're at the closest approach (and it needs to be pretty close), burn retrograde until Vel is close to zero. Trying to go into a circular orbit around Phobos is pretty much impossible, so don't bother. Then, fly around it like you would fly around a space station to get to your target docking port. Don't bother trying to use the slight hint of gravity to land, position yourself a meter or two above the pad and translate down until you get wheel stop.

To descend back to Mars, just goose the engines a bit to get clear of Phobos, set the orbit mfd reference to Mars, and burn retrograde. In all operations with Phobos and Deminos it's easier to think of them as space stations rather than a real moon like Earth's, their gravity is just nonexistant.

 

[PeterRoss]

I've made it all as I've said in this thread and in private: First I've made align and sync like while performing rendezvous with a vessel. When a few hundreds km left I've changed reference body in Orbit MFD to Phobos, pressed HUD button at Orbit MFD and manually turned ship retrograde. 30 seconds before periapsis I've started burn and easily reduced relative speed (Vel at Orbit MFD) to zero. After that I've activated HOLD LVL autopilot (looks like this AP uses 'distance to surface' criteria of choosing reference body rather than gravitational influence), lowered gears and send Deltaglider down at Phobos surface using RCS in Translation mode. Somewhere near 2 km of altitude I've passed through mesh surface and landed at the transparent sphere at the zero altitude. Relative gravitational influence of Phobos (as shown in Orbit MFD) at zero altitude was 0.02.

 

[Ark]

Yeah, not being able to land on non-spherical meshes sucks. I get around it by placing a Prelude with the mountain mesh on the surface, moving it around until I find a place where the asteroid mesh passes below the surface of the sphere, then fine-tuning until it looks convincing enough. On Phobos I put it on the side of the massive crater at one end. If you land on the pad and walk around, you can almost convince yourself you're standing on a landing platform. Until you walk off and find yourself in midair, that is.

 

[PeterRoss]

P.S. Notice that while performing retrograde burn the pro/retrograde vector will be moving. You have to change your movement vector accordingly.

---------- Post added at 06:53 PM ---------- Previous post was at 06:48 PM ----------

Yeah, not being able to land on non-spherical meshes sucks. I get around it by placing a Prelude with the mountain mesh on the surface, moving it around until I find a place where the asteroid mesh passes below the surface of the sphere, then fine-tuning until it looks convincing enough. On Phobos I put it on the side of the massive crater at one end. If you land on the pad and walk around, you can almost convince yourself you're standing on a landing platform. Until you walk off and find yourself in midair, that is.

I think when I'll get my hands on Mars (currently I'm building bases in Moon) I'll have to place Prelude on Phobos. Never used it before though.

 

[exe-c]

Yeh, finally I did it too but using a bit another method.
After launching and achiveing a rounded Mars orbit i set up a manouvre in TransX with a planechange included in it. My target was Daimos. Doing a MCC (a lot but very small about 2-10 m/s) i finally reach an orbit passing throught Daimos.
At the alt. about 50km i turned on lvl horizon autopilot and at alt 22km performed a hover burn. I noticed that when you falling directly to Daimos you orbital (Daimos) vel is equal you VS. So you may simply drop it to zero. Then I tuned my NAV translators to freq of Daimos base and perform a landing using VOR MFD and hover thrusters.
I had been continuing my martian system trip and visited Phobos using a same manouvre. When i returned to Olympus base on mars.

During that trip a one question arose. Why encounter data on the MFD (both Orbit or TransX) changing SO fast? For example - on TransX my Focus PJD has changed from 400m to 12k for about 10 seconds! Is Phobos/Daimos has an unstable orbit?

 

[2552]

No, it's just that Phobos/Deimos has so little gravity that your DG's main engine at full thrust will make huge changes to the displayed orbit on Orbit MFD in a very short time.

Edit: Or do you mean it's just changing that fast on its own? That's probably because of Mars' tidal forces pulling you and phobos slightly differently, changing your displayed orbit around Phobos, though I don't remember it happening that fast before

 

[exe-c]

Edit: Or do you mean it's just changing that fast on its own? That's probably because of Mars' tidal forces pulling you and phobos slightly differently, changing your displayed orbit around Phobos, though I don't remember it happening that fast before

Ye, on it's own during flight to it. They fluctuate in huge (compare to Phobos size) range - about 10km...